The above-cited patent application Ser. No. 07/154,469 relates to a method and apparatus for optical examination of an object, particularly by moire ray deflection mapping. The present application is directed to the extension of the basic setup described in that patent application so as to enable the apparatus also to operate as a Fizeau interferometer and also as a schlieren device, as well as a moire ray deflection mapper.
There are two different approaches to optical metrology, namely: interferometry, which measures phase retardation between two light beams, and ray-deflection analysis. The latter was first utilized in schlieren photography, and later in schlieren interferometry and moire deflectometry. patent application Ser. No. 07/154,469 describes an instrument which operates as a moire deflectometer. The invention of the present application shows how the basic telescopic instrument of that patent application can be used to produce an instrument which can operate independently not only as a moire deflectometer, but also as a Fizeau interferometer or as a schlieren device. As will be described more particularly below, such an instrument can be used in all three modes of operation without moving any optical components, and therefore offers a unique opportunity to compare the three methods. Moreover, the basic instrument can be used to operate according to all three methods simultaneously, and therefore the combinations of Fizeau and moire, moire and schlieren, and Fizeau and schlieren, can complement each other to produce improved results.
More particularly, the above-cited application Ser. No. 07/154,469 discloses a method, and also apparatus, for optical examination of an object involving the steps: providing a point source of light producing a diverging beam of direct light; directing the diverging beam of direct light to a first optical system including the object to be examined, which system retraces the light in the form of a beam of reflected light from the examined object back towards the point source of light; intercepting the converging beam of reflected light before reaching the point source of light; passing the intercepted converging beam of reflected light through a second optical system which collimates the beam of reflected light; and examining the collimated beam of reflected light. That patent application describes the use of the method for moire ray deflection mapping, wherein the examination of the collimated beam of reflected light is effected by directing the collimated beam through first and second gratings at a preselected angular orientation and distance with respect to each other to produce moire fringe patterns providing an indication of the properties of the examined object.